The present invention relates to improvements in a wire electric discharge machine in which a workpiece is machined by electric discharge generated between a wire electrode and the workpiece.
In wire electric discharge machining, a workpiece is machined by electric discharge generated when electric discharge energy is supplied between a wire electrode and the workpiece. A rate of electric discharge machining is approximately proportional to an intensity of electric discharge energy supplied between the wire electrode and the workpiece. In order to enhance the rate of electric discharge machining, it is necessary to supply electric discharge energy, the intensity of which is as high as possible, however, when the intensity of supplied energy is too high, breaking of the wire is caused, and it becomes necessary to connect the wire electrode again. As a result, the productivity of electric discharge machining is remarkably impaired.
Accordingly, in order to enhance the productivity of electric discharge machining of a wire electric discharge machine, it is necessary to input electric discharge energy, the intensity of which is as high as possible, while the intensity of electric discharge energy to be inputted is restricted in a range so that breaking the wire is not caused.
FIG. 6 is a schematic illustration showing an arrangement of a conventional wire electric discharge machine. For example, this arrangement is the same as that disclosed in Japanese Unexamined Patent Publication No. 62-19322. In FIG. 6, reference numeral 1 is a wire electrode, reference numeral 2 is a workpiece, reference numeral 3 is a wire bobbin, reference numerals 4a and 4b are flushing nozzles of dielectric fluid, reference numeral 5 is a capstan roller, reference numeral 6 is a pinch roller, reference numeral 7 is an X-table for driving the workpiece 2 in the horizontal direction (X-direction), reference numeral 8 is a Y-table for driving the workpiece 2 in the horizontal direction (Y-direction), reference numeral 9 is an X-axis servo amplifier for controlling a drive motor not shown for driving the X-table 7, reference numeral 10 is a Y-axis servo amplifier for controlling a drive motor not shown for driving the Y-table 8, reference numeral 11 is an electric power source used for electric discharge machining, reference numeral 12 is an electric discharge generation detecting means, reference numeral 13 is a pulse control means, reference numeral 14 is a calculation means, reference numeral 15 is a comparison means, and reference numeral 16 is a control means.
Next, operation will be explained below. The wire electrode 1 is held and drawn by the capstan roller 5 and pinch roller 6 so that the wire electrode 1 is made to travel. While dielectric fluid is being supplied in the working gap composed of the wire electrode 1 and the workpiece 2 from the flushing nozzles of dielectric fluid 4a, 4b, electric power for electric discharge machining, which is electric discharge energy, is supplied in the working gap from the electric power source 11 used for machining, and the wire electrode 1 and the workpiece 2 are moved relatively with each other by the X-table 7 and the Y-table 8 which are positioning means, so that the workpiece 2 can be machined by electric discharge. Positioning control for controlling the relative positions of the wire electrode 1 and the workpiece 2 conducted by the positioning means is governed by the control means 16, and also control of electric conditions conducted by the pulse control means 13 is also governed by the control means 16.
The electric power source 11 used for electric discharge machining applies a pulse-like voltage between the wire electrode 1 and the workpiece 2 according to control conducted by the pulse control means 13. The electric discharge generation detecting means 12 outputs a detection signal into the pulse control means 13 when electric discharge is generated between the wire electrode 1 and the workpiece 2. The pulse control means 13 stops supplying an electric current to the wire electrode 1 from the electric power source 11 used for machining after a predetermined period of time (pulse width) has passed from the input of a detection signal from the electric discharge generation detecting means 12. The calculation means 14 is inputted with a signal proportional to the pulse width from the pulse control means 13 and calculates its square. The thus calculated value is made to be an average machining electric current value. The comparison means 15 compares this average machining electric current value with an electric current limit which has been previously set as the maximum electric current value in a range in which wire breakage is not caused in the wire electrode 1. In the case where the average machining electric current value exceeds the electric current limit, the pulse control means 13 is controlled so that the average machining electric current value can not be higher than the electric current limit.
The conventional wire electric discharge machine is composed as described above, and the supply of a machining electric current is suppressed, the intensity of which is higher than that of the electric current limit which has been previously set as the maximum electric current in a range in which wire breakage is not caused. In this way, breaking of the wire is prevented in the wire electrode 1.
However, in the prior art described above, it is a problem how to determine the electric current limit. For example, it is obvious that it is harder to break the wire in a case in which the flushing nozzles of dielectric fluid 4a, 4b are arranged close to the workpiece 2 than in a case in which the flushing nozzles of dielectric fluid 4a, 4b are arranged distant from the workpiece 2. However, the conventional wire electric discharge machine does not distinguish a difference of the electric current limit caused by a difference in the relative position of the dielectric fluid nozzle with the workpiece described above.
Accordingly, the conventional wire electric discharge machine can not accurately control to avoid breaking the wire electrode by setting the electric current limit on the assumption that the relative position of the dielectric fluid nozzle with the workpiece is the same in the whole machining process. Therefore, in the case of machining a workpiece which is partly distant from the flushing nozzles, for example, in the case of machining across a counter bored hole which can be frequently seen in a die, if electric discharge clergy is supplied on the assumption that the dielectric fluid nozzle is arranged close to the workpiece, the breakage of the wire electrode is caused when a portion distant from the dielectric fluid nozzle is machined by electric discharge. If electric discharge energy is supplied on the assumption that the dielectric fluid nozzle is distant from the workpiece, it is impossible to obtain a sufficiently high rate of machining. The above problems may be encountered in the prior art.
When an end face or a step portion is machined by electric discharge, electric discharge is intermittently generated in many cases. Therefore, in the case of machining the end face or the step portion, it is necessary to reduce an intensity of electric discharge energy compared with a case in which machining is normally conducted. As described before, in the prior art, the electric current limit is set at a constant value which has been previously set before conducting electric discharge machining. When the electric current limit is set on the basis of the normal electric discharge machining condition, breakage of the wire electrode tends to occur in the case of conducting electric discharge machining on the end face or the step portion of the workpiece. When the electric current limit is set on the basis of conducting electric discharge machining on the end face or the step portion of the workpiece, the rate of electric discharge machining is remarkably lowered. The above problems are encountered in the prior art.
The present invention has been accomplished in order to solve the above problems. It is an object of the present invention to provide a wire electric discharge machine characterized in that: even when the relative layout of the nozzles with the workpiece varies or even when an end face or a step portion is subjected to electric discharge machining, the productivity of electric discharge machining can be greatly enhanced.
The present invention provides a wire electric discharge machine for conducting electric discharge machining on a workpiece by electric discharge generated in a working gap formed by a wire electrode and the workpiece by supplying electric discharge from a machining electric power source while a dielectric fluid is being supplied in the working gap formed by the wire electrode and the workpiece from flushing nozzles of dielectric fluid, comprising: normal electric discharge pulse detection means for detecting a normal electric discharge pulse in the working gap; normal electric discharge pulse calculation means for calculating normal electric discharge pulse energy from the detected normal electric discharge pulses; storage means for storing threshold value data in which a predetermined margin is ensured from an operation point at the time of wire breakage found from a relation between the normal electric discharge pulse energy and the electric discharge machining energy setting value corresponding to various electric discharge machining conditions; and control means for controlling the electric discharge machining energy setting value so that the operation point can approach the threshold value data.
The present invention provides a wire electric discharge machine, wherein as a parameter for changing the electric discharge machining energy setting value controlled by the control means, at least one of the parameters for setting an electric discharge frequency such as a pause time and servo reference voltage is used, and the threshold value data are set from a relation between the parameter and the normal electric discharge pulse energy.
The present invention provides a wire electric discharge machine, wherein as a parameter for changing the electric discharge machining energy setting value controlled by the control means, at least one of the parameters for setting electric discharge energy per one pulse such as a peak electric current setting value and a pulse width is used, and the threshold value data are set from a relation between the parameter and the normal electric discharge pulse energy.
The present invention provides a wire electric discharge machine for conducting electric discharge machining on a workpiece by electric discharge generated in a working gap formed by a wire electrode and the workpiece by supplying electric discharge energy from a machining electric power source while a dielectric fluid is being supplied in the working gap formed by the wire electrode and the workpiece from a dielectric fluid nozzle, comprising: normal electric discharge pulse detection means for detecting a normal electric discharge pulse between the electrodes; normal electric discharge pulse counting means for counting the number of normal electric discharge pulses from the detected normal electric discharge pulses; storage means for storing threshold value data in which a predetermined margin is ensured from an operation point at the time of wire breakage found from a relation between the number of normal electric discharge pulses and the pause time setting value corresponding to various electric discharge machining conditions; and control means for controlling the electric discharge machining energy setting value so that the operation point can approach the threshold value data.
The present invention provides a wire electric discharge machine, wherein the electric discharge machining conditions include a difference in a relative position between the electric discharge machining nozzle and the workpiece.
Since the wire electric discharge machine of the present invention is composed as described above, the following effects can be provided. Even when the relative layout of the nozzles with the workpiece varies or even when electric discharge machining is conducted on an end face or step portion of the workpiece, it is possible to supply electric discharge energy, the intensity of which is very close to a critical value where wire breakage occurs. Therefore, it is possible to provide a wire electric discharge machine, the productivity of electric discharge machining of which can be greatly enhanced.